System and method for tuning a radio receiver

An integrated circuit for tuning an FM radio, the integrated circuit comprising:

• an FM radio receiver including a local oscillator configured to receive a combined local oscillator control signal and generate a local oscillator frequency, a mixer configured to mix the local oscillator frequency and an FM radio input signal to generate a downconverted signal, an analog to digital converter (ADC) configured to digitize the downconverted signal and to provide a digitized signal, and a demodulator configured to receive the digitized signal and generate a digital error signal and a baseband signal including FM radio information;
• a digital synthesizer circuit configured to generate a first local oscillator control signal corresponding to an estimate of a desired local oscillator frequency, the digital synthesizer circuit including a counter configured to receive a reference frequency and an output of the local oscillator, a digital accumulator configured to receive and accumulate an output of the counter, and a synthesizer scaling element configured to receive the accumulated output;
• a digital automatic frequency control (AFC) circuit configured to receive the digital error signal and generate a second local oscillator control signal corresponding to the desired local oscillator frequency, the digital synthesizer circuit being enabled to generate the local oscillator control signal when the digital AFC circuit is disabled, the digital AFC circuit being enabled to generate the second local oscillator control signal when the digital synthesizer circuit is disabled;
• and
• a combining element combining the first local oscillator control signal and the second local oscillator control signal to form the combined local oscillator control signal.

A tangible computer-readable medium having stored thereon computer-executable instructions that, if executed by one or more computing devices, cause the one or more computing devices to perform operations comprising:

• generating a first local oscillator control signal corresponding to a desired local oscillator frequency when a second local oscillator control signal is disabled, generating the first local oscillator control signal including providing a signal representing a frequency difference between a reference frequency and an output of a local oscillator, providing the signal representing a frequency difference between a reference frequency and the output of a local oscillator to a digital accumulator, storing in the digital accumulator the signal representing a frequency difference between a reference frequency and the output of a local oscillator, and scaling the stored signal to develop a time constant for the first local oscillator control signal;
• generating the second local oscillator control signal when the first local oscillator control signal is disabled;
• and
• combining the first local oscillator control signal and the second local oscillator control signal to form a combined local oscillator control signal.

An FM radio receiver for tuning to channels in an FM frequency range, the FM radio receiver comprising:

• computer hardware including at least one computer processor;
• and
• computer-readable storage including computer-readable instructions, that when executed by the computer processor, cause the computer hardware to perform operations defined by the computer-executable instructions, the computer-executable instructions including:
• generating a first local oscillator control signal corresponding to a desired local oscillator frequency when a second local oscillator control signal is disabled, generating the first local oscillator control signal including providing a signal representing a frequency difference between a reference frequency and an output of a local oscillator, providing the signal representing a frequency difference between a reference frequency and the output of a local oscillator to a digital accumulator, storing in the digital accumulator the signal representing a frequency difference between a reference frequency and the output of a local oscillator, and scaling the stored signal to develop a time constant for the first local oscillator control signal;
• generating the second local oscillator control signal when the first local oscillator control signal is disabled, generating the second local oscillator control signal including accumulating a digital error signal, scaling the accumulated digital error signal to develop a time constant for the second local oscillator control signal;
• and using the accumulated digital error signal to generate the second local oscillator control signal;
• and
• combining the first local oscillator control signal and the second local oscillator control signal to form a combined local oscillator control signal.